This invention relates to coating shaped articles and, more particularly, to applying orthophosphate coatings to films.
U.S. Pat. No. 3,821,014, to Haskell and Hecht, teaches the application of aluminum orthophosphate coatings to shaped objects such as films to achieve extraordinarily high moisture vapor and oxygen-barrier properties. It is disclosed to deposit the aluminum orthophosphate onto the film surface by the reaction of a phosphate compound such as phosphoric acid with an anion compound of aluminum such as aluminum chloride or aluminum chlorhydroxide, wherein the anion is the chloride ion. The patent stresses the need for removal of the HCl or chloride ion to insure good barrier properties but suggests it is not generally necessary when aluminum chlorhydroxide is used instead of AlCl.sub.3. The patent indicates that excessive chloride ion removal from the dispersion causes premature gelation. The method disclosed for removal of chloride ion is dialysis or ion exchange resin treatment of the aqueous dispersion before application to the film. The orthophosphate coating is then dried at temperatures which effect a substantially complete cure thereof.
U.S. Pat. No. 3,853,588, to Haskell and Hecht, discloses the topcoating of orthophosphate-coated films with a vinylidene chloride copolymer containing about 2 to 30% of a polymeric epoxy resin to improve barrier properties under moist conditions.
U.S. Pat. No. 3,853,591, to Haskell, Hench and Yates, discloses the use of tin ions, among others, as a partial substitute for aluminum in the orthophosphate to further improve barrier properties.